What you’re experiencing is sometimes referred to as a double engagement of the transmission. The problem is due to a defective valve body that wants to be replaced. I think there is a note about it on alldata.com. I have seen others comment on it here. You might do a search for double engagement
The delay in upshifting when cold is by design, as others have stated.
'00 ML320 "Casper"
'92 400E "Stella"